Showing papers on "Fresnel zone published in 1974"
TL;DR: In this article, phase reversal zone plates are designed for regions of the electromagnetic spectrum where the index of refraction is complex, with a real part close to 1.0, and materials with suitable optical and mechanical properties exist throughout most of the 1-800-A wavelength range for their construction.
Abstract: Phase-reversal zone plates can be designed even for regions of the electromagnetic spectrum where the index of refraction is complex, with a real part close to 1.0. These devices are superior to Fresnel zone plates both in their light collection, and in their signal-to-noise characteristics. Materials with suitable optical and mechanical properties exist throughout most of the 1–800-A wavelength range for their construction. Imperfections in fabrication, such as incorrect plate thickness, sloping zone edges, or an error in the width of alternate zones result in only moderate deterioration in optical performance.
403 citations
TL;DR: The Fresnel diffraction pattern of a grating periodically gives an exact reproduction of the grating that depends upon the degree of parallelism of the incident beam, and the possibility of using this technique for studying the focusing errors in a collimating lens or a mirror is presented.
Abstract: The Fresnel diffraction pattern of a grating periodically gives an exact reproduction of the grating. By superposing a second grating on such an image, we form a moire pattern that depends upon the degree of parallelism of the incident beam. We present here the possibility of using this technique for studying the focusing errors in a collimating lens or a mirror.
62 citations
TL;DR: A developed form of the Fresnel zone-plate interferometer is described, associated with the real and virtual first order foci of a zone plate, and its properties are discussed.
Abstract: A developed form of the Fresnel zone-plate interferometer is described. Three basic configurations are distinguished, associated with the real and virtual first order foci of a zone plate. Related versions and higher order variants are also educed. Compensated phase zone plates used in this application are found to produce uniform amplitude wavefronts. The properties of the interferometer in this form are discussed and an example given of its high-quality performance.
56 citations
Patent•
28 Jun 1974
TL;DR: An ultrasonic transducer system comprises a one or two dimensional array of transducers which are subdivided into groups as discussed by the authors, and operate simultaneously in a manner to produce acoustic energy beams which provide an interference pattern in the near-field focal zone.
Abstract: An ultrasonic transducer system comprises a one or two dimensional array of transducers which are subdivided into groups. The groups are selected and operated simultaneously in a manner to produce acoustic energy beams which provide an interference pattern in the near-field focal zone. The groups, moreover, are shifted incrementally along a predetermined direction to provide a scan along a workpiece surface. The transducer system, operating in a manner similar to a Fresnel zone lens, yields greatly improved image resolution, particularly when used in conjunction with a B- or C-scan presentation.
47 citations
TL;DR: Experimental focal plane intensity distributions are presented for a 10-zone acoustic zone plate operating at approximately 10 MHz in this article, where the results are related to the spatial frequency response of the transducer.
Abstract: Experimental focal plane intensity distributions are presented for a 10‐zone acoustic zone plate operating at approximately 10 MHz. The results are related to the spatial frequency response of the transducer. Some initial imaging experiments with this transducer are described along with preliminary results for an acoustic phase plate.
41 citations
TL;DR: It is shown that the largest SNR advantage occurs for a point source, while for very large, uniform sources there may be a slight net disadvantage to using a zone plate, and that optical processing does not give the highest possible SNR.
Abstract: A Fresnel zone plate, used as a coded aperture, offers a great advantage in geometric collection efficiency over a conventional pinhole or collimator. We present a detailed analysis of the signal-to-noise ratio (SNR) of a quantum-limited zone plate camera. The magnitude and spatial distribution of the noise field and its dependence on the source distribution and the characteristics of the optical processing system are derived. It is shown that the largest SNR advantage occurs for a point source, while for very large, uniform sources there may be a slight net disadvantage to using a zone plate. It is also shown that optical processing does not give the highest possible SNR.
40 citations
TL;DR: The theory of optical propagation through atmospheric turbulence demonstrates the sensitivity of such quantities as log-amplitude variance and covariance to strength of refractive turbulence and transverse wind by using a crossed-path technique to derive path profiles of these quantities.
Abstract: The theory of optical propagation through atmospheric turbulence demonstrates the sensitivity of such quantities as log-amplitude variance and covariance to strength of refractive turbulence and transverse wind. We exploit this sensitivity by using a crossed-path technique to derive path profiles of these quantities. The results are insensitive to changes in the spatial spectrum of the refractive-index variations. The path resolution is easily varied by changing the receiver and transmitter separations and is ultimately limited by signal-to-noise considerations. The experimental results for horizontal paths, described here, will ultimately be used to indicate the feasibility of profiling on vertical paths with passive sources.
34 citations
TL;DR: In this article, the use of tapered reflectivity mirrors and shaped apertures in unstable resonators is shown to be an effective method for improving the mode properties of a resonator, where mode intensity and phase profiles are smoothed and the mode discrimination ratio is increased.
Abstract: The use of tapered reflectivity mirrors and shaped apertures in unstable resonators is shown to be an effective method for improving the mode properties. Mode intensity and phase profiles are smoothed and the mode discrimination ratio is increased. Results are presented illustrating the importance of diffracted waves from sharp mirror edges in determining these mode properties. A simple expression for estimating the diffractive contribution is given and is used to determine optimum mirror designs. Shaped mirrors and mirrors having amplitude and phase reflectivity tapers are studied. The concept of equivalent Fresnel zones is used to gain physical insight into the mode properties.
24 citations
TL;DR: Experiments performed with a stable single-mode Nd(3+)-YAG laser demonstrate that the MZP can be important tool for laser machining purposes and a simple method of recording wavelength-shift corrected in-line holograms is described.
Abstract: Machining of small holes with arbitrary contours can be performed by focusing a laser beam with a modulated zone plate (MZP). MZP's use the structure of the Fresnel zone plate as the carrier of a modulation function, which contains complete information about the contour to be machined. Spherically corrected MZP's produce aberration-free images within a field angle of 10(-3) rad. It is shown that the background noise due to higher diffraction orders is unimportant under typical machining conditions. A manufacturing procedure for high resolution MZP's with up to 2500 zones etched in chromium or quartz layers deposited on glass substrates is discussed. As in-line holograms have properties similar to MZP's, a simple method of recording wavelength-shift corrected in-line holograms is described. Experiments performed with a stable single-mode Nd(3+)-YAG laser demonstrate that the MZP can be important tool for laser machining purposes.
23 citations
TL;DR: A two-step autoradiographic imaging technique utilizing a coded aperture in the form of a lead on-axis Fresnel zone plate is presented, and several isotope-filled plastic phantoms were successfully imaged.
Abstract: A two-step autoradiographic imaging technique utilizing a coded aperture in the form of a lead on-axis Fresnel zone plate is presented. Several isotope-filled plastic phantoms were successfully imaged. These images contain tomographic information of very good quality. The advantages and disadvantages of the technique are discussed.
12 citations
TL;DR: In this paper, a theoretical investigation of the imaging of extended objects using a Fresnel zone plate as a coded aperture with coherent-optical image reconstruction is presented, where artifacts are introduced in the images of large objects.
Abstract: A theoretical investigation of the imaging of extended objects is presented using a Fresnel zone plate as a coded aperture with coherent-optical image reconstruction. Faithful images are obtained only for small objects; artifacts are introduced in the images of large objects. Attempts to increase image fidelity are shown to be only moderately successful.
01 Mar 1974
TL;DR: In this article, a variety of closely related coded apertures, including an annulus, an inverted zone plate, a spiral zone plate and the Girard grill, are discussed.
Abstract: Mertz and Young introduced the idea of using a Fresnel zone plate as a shadow-casting reticle, or coded aperture, in x-ray astronomy. More recently, considerable progress has been made toward using the zone-plate aperture for gamma-ray imaging in nuclear medicine. The most successful configuration has used an off-axis section of a zone plate in conjunction with a halftone screen. In this paper, we discuss a variety of closely related coded apertures, including an annulus, an inverted zone plate, a spiral zone plate and the Girard grill. In most cases, the technique of grid-coded subtraction is used to suppress the zero-order (DC) background light usually associated with zone-plate imaging. The first application of this technique, reported by Stoner et al., used a sequence of two to four on-axis zone plates. In the present paper it is shown that the method can be extended to other apertures and is also very useful in synthesizing the spatial filters for optical decoding.
TL;DR: In this paper, a point source focused by a Fresnel zone plate may interfere constructively or destructively with the undiffracted background, and the point source with unusually small dark centers empirically leads to constructive interference.
01 Oct 1974
TL;DR: In this paper, the power transfer efficiency between two elliptical antennas in the Fresnel zone is investigated experimentally, where pyramidal horns in the foci of the ellipsoids enable an optimum phase illumination.
Abstract: The power transfer efficiency(ratio of received to transmitted power) between two elliptical antennas in the Fresnel zone is investigated experimentally. The design procedure for an optimum power transfer system is analyzed. Pyramidal horns in the foci of the ellipsoids enable an optimum phase illumination. Deviations from a Gaussian amplitude illumination (which is close to the optimum) cause a significant decrease of the efficiency, which however is still larger than it would be for a guided or a free path transmission in the far-field of two antennas.
01 Nov 1974
TL;DR: In this article, a simple Fresnel corrected geometric optics model for the surface-scatter channel is proposed to explain the unusually high deggee of dispersive scattering observed, and the shape of the scattering function for the channel is derived and its shape shown to be range dependent for wide beam excitation.
Abstract: Many communication channels involving distortion due to random time-varible surface scattering suffer from extremely acute time and frequency smear. This is particularly true for sonar and low or medium frequeacy electromagnetic propaption where Fresnel zones can be large and yet where Rayleigh parameters can also be quite high. Using a simple Fresnel corrected geometric optics model for the surface-scatter channel, it is possible to explain the unusually high deggee of dispersive scattering observed. The Scattering function for the channel is derived and its shape shown to be range dependent for wide beam excitation. Under certain not unreasonable assumptions about the surface statistics this function is, in fact, shown to exhibit a narrow parabolic ridge with a "hollow" interior.